(1) Field of the Invention
The present invention relates to a thermosetting resin composition for a powder paint and a thermosetting powder paint composition using the same. More particularly, the present invention relates to a thermosetting powder paint composition which has excellent storage stabilites (blocking property and the like), appearance properties (cissing, smoothness, sharpness and the like), physical properties (hardness, scratch-resistance and the like) and chemical properties (weather-resistance, acid-resistance, solvent-resistance and the like) and particularly can provide a baked paint film suitable for vehicle painting use.
(2) Description of the Prior Art
Conventionally, solvent type paints are used for painting articles, and paints satisfying various requirements for use in fields such as automobiles and the like in which strict qualities are required have been developed and used.
Recently, in the technical field of paints, change from solvent type paints to powder type paints (hereinafter, referred to as powder paint) has been expected from the standpoints of local or global environmental protection (VOC (volatile organic compound) restriction), labor safety hygiene environment improvement, fire and explosion protection, resources saving and the like.
Along increase in expectation of high ability and variety of powder paints owing to historical or social requirements, powder paints have also been required to reveal high-grade paint film abilities (e.g., weather-resistance, acid rain-resistance, scratch-resistance and the like) corresponding to those of solvent type paints. However, irrespective of increased strictness of paint film abilities required for powder paints, it is not necessarily admitted that powder pants completely satisfying these requirements have been available commercially. Specific examples of conventional type powder paints include epoxy resin powder paints and polyester resin powder paints. However, these paints had problems not only in weather-resistance but also in resistance to acid rain which has been recently regarded as problematical, and had problems in the field of automobile body painting and the like.
For improving these defects, U.S. Pat. No. 3,954,898 (Japanese Patent Application Publication (JP-B) No. 48-38617) suggested an acrylic powder paint and remarkable improvement in weather-resistance was realized. Thereafter, a lot of studies have been made regarding acrylic powder paints. However, these acrylic powder paints did not fully satisfy simultaneously appearance properties, physical properties, chemical properties and storage stabilities, particularly, smoothness and blocking property. For improving smoothness, it is most effective to decrease the melt viscosity. However, the glass transition temperature should be lowered to decrease the melt viscosity, and in this method, satisfying both smoothness and blocking property was impossible.
Then, there has been suggested a resin composition which has improved smoothness by mixing a thermosetting resin having high melt viscosity and high glass transition temperature with a thermosetting resin having low melt viscosity and low glass transition temperature, the latter resin having different solubility parameter from that of the former resin (Japanese Patent Application Laid-Open (JP-A) No. 8-209034). However, this resin composition revealed reduced appearance properties (cissing, smoothness) and storage stability (blocking property) and the like due to dispersion failure and localization phenomenon during storage, and did not manifest satisfactory effects, since resins having different solubility parameters were physically mixed.
Usually, a flow controlling agent is used in an acrylic powder paint for the purpose of improving smoothness and preventing cissing (cratering, fish eye). Paints or resin composition in which appearance properties, physical properties and chemical properties are improved by a flow controlling agent have been suggested (JP-A No. 57-49672, U.S. Pat. Nos. 5,523,349, 5,648,117 (JP-A No. 7-179789) and the like). However, these resin compositions also revealed reduced appearance properties (cissing, smoothness) and storage stability (blocking property) and the like due to dispersion failure and localization phenomenon during storage, and did not manifest satisfactory effects, since a flow controlling agent was only physically mixed by a melt kneading method and the like.
Further, there have been suggested compositions in which a reactive functional group such as an amino group, carboxyl group, hydroxyl group, epoxy group and the like is contained, as a reactive flow controlling agent, in the molecule and this agent is reacted with a main component or curing agent component in forming a paint film to improve paint film properties (U.S. Pat. No. 5,212,245 (JP-A No. 8-325480), WO 97/30131 (Japanese Kohyo Patent Publication 11-506156) and the like). However, this reaction is only a reaction in forming a paint film, and there is almost no reaction in the paint composition and improvement in dispersibility of a flow controlling agent owing to the reaction is not considered. Therefore, these flow controlling agents also provided reduced appearance properties (cissing, smoothness) and storage stability (blocking property) and the like due to dispersion failure and localization phenomenon during storage, and did not accomplish satisfactory effects, similar to the flow controlling agents of the conventional type.
Furthermore, there has been suggested powder paints in which appearance property (smoothness) is improved by allowing a silicon component as a G (branch) block to graft-react with an acrylic vinyl copolymer component as a S (back bone) block as a technology for grafting a G (branch) block to a S (back bone) block (WO 95-15347(Japanese Kohyo Patent Publication 9-505847) and the like). This technology is apparently different from the instant application in which a G (back bone) block is a silicon component and a G (branch) block is a vinyl-based polymer, and particularly, preferably an acrylic vinyl polymer. Further, this powder paint had a problem in re-coating property since the silicon component reduces excessively the critical surface tension of the paint film surface layer.